What Are they? The Adjustable rear (tie/control) arms are used in order to tackle the lack of camber adjustment, especially noticeable when the vehicle has been lowered (pic below).

Forge Motorsport are selling adjustable rear arms with added adjustment and added strengthening. Then polyurethane bushes were used because they offer far better characteristics than plastic ones. If you ignore the obvious benefits of reducing uneven tire wear and improving the tire surface contact area, the seat of the pants ride is far better.

Although the top tie/control arms have been left as standard, the plastic bushes on them have been up-rated to the  polyurethane bushes made by www.Powerflex.co.uk